We are all familiar with images of satellites orbiting
the earth, bristling with masts, antennae and solar array systems. However,
most of these accessories not only have to be neatly packaged up for their journey
into space but also have to unpack themselves correctly once in orbit. Failure
to do so can severely reduce the capability of a satellite, as happened in the
recent Galileo project, or can even lead to the complete loss of a mission.
Dr Sergio Pellegrino and his group are tackling the problems of packaging and
unfolding these deployable structures.

Many of the packaging solutions resemble intricate works
of origami. Pellegrinos laboratory is littered with fascinating examples, such
as folding patterns for solar sails and foldable cylinders, which are broken
up into triangles, thus allowing them to be squashed flat.

Triangular pantographic mast, folded and deployed.

Controlled and unconstrained

Two types of deployment strategy are used in this field:
controlled deployment, where a structure is expanded by actuators or motors,
and unconstrained deployment, which is driven by the release of elastic strain
energy stored within the structure during folding.

Controlled deployment has been used by the group in the
development of a novel concept for folding rigid-surface antennae, where the
panels of the antennae are controlled by simple mechanical joints. Another novel
concept is for the controlled deployment of large-mesh reflectors, by means
of a deployable ring.

Work on unconstrained deployment is currently concentrated
on analysing the deployment sequence of a collapsible rib-tensioned surface
reflector. This reflector is similar to an umbrella, with flexible ribs connected
to a central hub. It is packaged by folding the ribs into a zig-zag pattern
and deployed by letting the ribs go. By using computer simulations of the unfolding
process, different methods of packaging and various rib cross-sections can be
used to prevent the structure unfolding into an incorrect configuration.

Another area of activity in the group is vibration control
in large flexible structures. Applications include the stable mounting of a
camera at the tip of a deployable mast, and using active control to minimise
vibration induced during the deployment of a solar array.

The Deployable Structures research is sponsored by British
Aerospace, The Royal Society, the European Space Agency, the EPSRC and the Cambridge
Commonwealth Trust.